An injection molding machine and a die cast machine mainly include a mold clamping device and an injection device. A mold including a fixed mold and a movable mold is closed by a mold clamping device and a cavity, which is a hollow space having the shape of a product, is formed therein, and plastic or aluminum in a molten state is injected into and filled in the cavity by the injection device and after the molten material has cooled and solidified, the mold is opened and a molded article (product) is obtained.
The mold clamping device opens/closes a mold by reciprocating the movable mold and is capable of exerting a strong mold clamping force in the state where the mold is closed. By exerting the mold clamping force, it is possible to prevent the mold from opening while resisting the pressure under which plastic, etc., in the molten state is injected into and filled in the mold. Further, the structure is such that it is possible for an operator to remove the molded product from the movable mold and take the molded product out of the machine in the state where the mold is open.
As described above, the mold clamping device is operated to open/close the mold and exerts the mold clamping force, and therefore, the device is surrounded by a door, etc., to prevent an operator from entering the device during molding. A door includes a fixed door attached fixedly and a safety door that can be opened/closed to allow a molded product to be taken out of the machine and a mold to be carried in/out in the transverse direction using a set-up device. A horizontal type mold clamping device has a structure in which the safety door is located in the transverse direction of the mold, a wheel, etc., is attached to the safety door, and the safety door can be slid (opened/closed) in the reciprocating direction of the movable mold.
In a molding process, in order to take out a molded product from the machine in the transverse direction, it is necessary to open/close the safety door each cycle, which requires a lot of labor for an operator to open/close the safety door (particularly, in the case of a large machine with a heavy door), and therefore, a safety door automatic opening/closing device that makes use of an air cylinder is used frequently to reduce the labor and is installed in most large machines.
FIG. 6 shows a horizontal mold clamping device with a general toggle link mechanism, in which a safety door automatic opening/closing device is installed. On a machine base 9, a fixed platen 4 that holds a fixed mold 1 is fixed, and a movable platen 5 that holds a movable mold 2 is mounted movably on the left side thereof. Further, on the left side of the movable platen 5, a link housing 6 and a link mechanism 6a are provided, which open/close the movable platen 5 and exert a mold clamping force. On the right side of the fixed platen 4, an injection device is installed, which injects and fills plastic or aluminum in the molten state in the mold.
To the lateral side of the link housing 6 and the link mechanism 6a of the mold clamping device, a fixed door 12 is attached fixedly, which cannot be opened, except for maintenance, such as machine repair.
On the other hand, to the lateral side of the fixed mold 1, the movable mold 2, and the movable platen 5, a safety door 11 is attached and can be opened/closed in the transverse direction by the action of a wheel etc.
Further, under the safety door 11, an automatic opening/closing device 13 is attached to the machine base 9 and the safety door 11 can be opened/closed automatically (without the labor of an operator) via a coupling part 17. In the automatic opening/closing device 13, an air cylinder is used usually as a drive device, and the main body part of the air cylinder is fixed on the machine base 9 and at the same time, the coupling part 17 is attached to the tip end part of a cylinder rod and coupled with the safety door 11.
To the end surface on the side in the direction of travel of the safety door 11 in the closing operation, a touch switch 18 is attached. This is a safety device to prevent an operator who is still in the device from being sandwiched in the closing operation, and when electrically detecting contact with the operator in the closing operation, a controller operates an air valve, etc., to immediately stop the closing operation, and then subsequently changes the operation to the opening operation.
FIG. 7 shows a state where the mold is open and the safety door 11 is fully open.
The opening/closing stroke of the safety door is determined to a length so that the safety door can be opened to a position where an operator can inspect and repair the cavity surface of the opened mold or the side surface of the mold when the molding operation comes to rest. Then, in designing the automatic opening/closing device, an air cylinder with a length that can realize this opening/closing stroke is selected.
Due to the characteristics of the air cylinder, it is difficult to stop the cylinder rod at a position set on the way of the stroke with high precision in an expanding/contracting operation of the cylinder rod. Because of this, it is difficult to stop the safety door at a position other than the fully opened position and the fully closed position of the safety door, where the cylinder rod is located on both the stroke ends. Consequently, in the molding process also, it is necessary to open the safety door to the fully opened position and close to the fully closed position (the entire stroke) for each cycle.
However, in order for an operator to take out a molded product in the molding cycle, it is only necessary that part of the body of the operator (arm, upper part of the body, etc.) can be put into the mold clamping device to grasp and carry out the molded product, and therefore, it is not necessary to open the safety door through the entire stroke. Further, also when a mold is carried in/out of the device using a mold set-up device (in the set-up process), the door needs to be open slightly wider than the width through which the closed mold can be passed, and therefore, it is not necessary to open the safety door through the entire stroke. In particular, the larger a molding machine is, the longer the excessive opening/closing stroke of the safety door is, and therefore, the wasteful time (waiting time) becomes longer.
Due to the above, an attempt has been made to shorten the cycle time and the set-up time by shortening the opening/closing operation stroke by stopping the operation on the way instead of opening through the entire stoke with an air cylinder.
As one of the methods, Patent Literature 1 discloses a method of adjusting the open position of a safety door in accordance with the amount of opening of a movable platen and a mold.
With this method, it is possible to electrically detect the relative position of the movable platen and the safety door by attaching a limit switch to the safety door and at the same time, attaching a dog to the movable platen. When an electric signal from the limit switch is detected during the opening operation of the safety door, the air valve is operated to limit the supply of air pressure to the air cylinder. Due to this, it is possible to reduce the speed of the opening operation of the safety door and stop the safety door at a position in accordance with the open position of the movable platen.                [Patent Literature] Japanese Unexamined Patent Publication (Kokai) No. 08-25448        
However, with the method according to Patent Literature 1, although it is possible to determine an open position of the safety door in accordance with the amount of opening of the movable platen, it is necessary to manually adjust the position of the limit switch when desiring to further make a fine adjustment in accordance with the shape of the molded product. Further, it is necessary to attach another limit switch or dog in order to stop the safety door at a minimum necessary open position in the set-up process.
Next, in order to shorten the cycle time, it is necessary to open/close the safety door in a brief time both speedily and accurately. However, the operation by the air cylinder can be set to only two levels at the most, i.e., high speed and low speed, and it is difficult to freely set the speed, and control the speed and acceleration/deceleration (at the most, only the air throttle valve can be adjusted), and therefore, it is difficult to quickly open/close the safety door and shorten the cycle time thereby.
Further, in order to secure the safety of an operator, it is necessary to attach a touch switch to the end surface in the direction of travel at the time of the closing operation. However, if a touch switch is attached to the safety door, it is difficult to wire it to the controller and at the same time, the cost is increased.